Hello Ahmedlmad
Typically, the reason for not using LDP for BGP prefixes is due to the use of BGP itself for label distribution in MPLS networks, more specifically through an extension of BGP known as Multiprotocol BGP or MP-BGP.
MP-BGP is used when MPLS is employed over BGP because it supports multiple network layer protocols, not just IPv4. This includes the distribution of label information using BGP NLRIs.
For the specific case of VPNs, BGP is used to distribute VPN label information between PE routers, enabling MPLS VPN services over BGP.
The key reason behind this is control and flexibility. BGP allows more control over path selection based on policy (as opposed to just shortest-path), and allows the network to scale to larger sizes. When running MPLS in conjunction with BGP, network engineers have greater flexibility and control over traffic engineering, quality of service, and other advanced features. BGP also allows for complex scenarios like inter-AS MPLS VPNs.
So to conclude, labels aren’t generated for BGP prefixes with LDP because BGP itself (more specifically, MP-BGP) is used to handle label distribution for these prefixes. Does that make sense?
I hope this has been helpful!
Laz